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Everglades Restoration Program (RECOVER 2004; 2006; Robblee and Browder 2012).
Seagrass, algae and associated environmental and physical measurements collected in
FIAN are coupled with data available from other environmental agencies. The primary
objectives are: 1) to characterize the seagrass community (e.g., species composition,
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cover-density, and distribution); and 2) to characterize the environmental and physical
conditions (e.g., surface and bottom salinity and temperature, turbidity, sediment depth,
and water depth) observed in POM; 3) to determine if there are relationships between the
seagrass community and the environmental and physical conditions in POM; and 4) to
evaluate if the natural and/or anthropogenic changes documented during the study period
have influenced the seagrass habitat in POM.
Hypothesis 1: There are short and long term temporal and spatial changes evident in
the seagrass composition, cover-density, and distribution within the Port of Miami.
The Port of Miami, within North Biscayne Bay, has been influenced by
development in Miami and expansion of the major shipping port within the last century.
Areas with high human activity are prone to more drastic and frequent changes than other
less populated areas. This can alter water quality within a system and impact the benthic
habitat. The seagrass habitat in Port of Miami will be assessed to evaluate whether there
has been a decline in seagrass composition, cover-density, or distribution over time.
Hypothesis 2: There are short and long term temporal and spatial changes evident in
the environmental and physical conditions in the Port of Miami.
A natural cycle of weather events occur in South Florida, creating two distinct
seasons (dry and wet). The amount of rain and storm activity can be severe some years
and can in turn cause changes to the environmental and physical conditions (e.g. water
depth, sediment depth, temperature, salinity, and turbidity) within the coastal habitats.
The extent of these environmental and physical changes in the system will be assessed.
Hypothesis 3: Changes in the environmental and physical conditions within the Port of
Miami relate with changes in the composition, density and distribution of the benthic
community.
Short and long-term changes in quality of the water within a system can impact
the benthic habitat. Trends/associations between the seagrass and environmental and
physical data will be assessed within the basin.
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Hypothesis 4: Natural and anthropogenic influences have caused changes to the
seagrass habitats within the Port of Miami over time.
Seagrass communities in North Biscayne Bay have been highly variable because
of habitat modifications that have been taking place since the early 1900s (Caccia and
Boyer 2005). Human activities and development, as well as natural events, stress the
nearshore coastal marine environments in South Florida. Areas with high levels of
human activity are at greater risk for unnatural habitat disturbances.
2.0 Materials and Methods
Data used for this study come from an existing data set developed in the South
Florida Seagrass Fish and Invertebrate Network, FIAN (Robblee and Browder 2012) (see
Table 2). Data are located on the USGS Benthic Database maintained by Everglades
National Park. As a Monitoring and Assessment Plan project, FIAN is part of
RECOVER, the Restoration, Coordination and Verification Program of the
Comprehensive Everglades Restoration Plan (CERP) (RECOVER 2004; USACE and
SFWMD1999).
2.1 FIAN Data
The FIAN project sampled 19 basins in three regions of South Florida: Biscayne
Bay, Florida Bay, and the Lower Southwest Mangrove Coast. For this study of Port of
Miami, data from one of the nineteen FIAN locations (POM) are used in analyses (Figure
2). To assess changes between sampling years and season, samples were collected at the
end of the spring (dry season Apr/May) and fall (wet season Sept/Oct) from 2005 through
2011, for a total of fourteen collections. Using a geographic information system (GIS), a
grid of 30 equal-sized cells was superimposed over the basin (Figure 3) to encompass the
observable or expected gradients of physical and environmental conditions and
vegetation characterizing the location. The sample grid-cells only encompassed waters
that were accessible to a shallow-draft boat (Robblee and Browder 2012). Within each
cell a single randomly located point was sampled. This method allowed FIAN the ability
to randomly, but quasi-evenly, sample the environmental and habitat gradients present in
an area and still create an accurate representation of the entire basin. The grid-cell size
sampled in the Port of Miami covered a total of 1060.5 hectares (10,605,000 m2
) across
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the basin. A total of 420 samples were collected for analysis in the basin during the 7
years of FIAN.
2.1.1 Seagrass Community Vegetation Sampling
A Garmin GPSMAP492 GPS was used to locate each sampling sample site and
the latitude and longitude coordinates were recorded. The vegetation observations and
sediment composition were recorded by a free-diving researcher. A modified BraunBlanquet cover-abundance method was used to quantify the seagrass and algae in a 0.25
m2
quadrat at each site (Braun-Blanquet 1932; Mueller-Dombois and Ellenberg 1974;
Fourqurean et al. 2002). This method involves classifying all vegetative species present
and assigning an abundance code for each species present (Braun-Blanquet 1932). This
allows for large areas to be sampled in a short time (Wikum 1978), while still accurately
representing the overall vegetation composition. Braun-Blanquet is a useful tool for
establishing baseline data for assessment of environmental impacts (Wikum 1978).
Replicate quadrats were sampled at each individual site within a basin, and a coverabundance rating from 0 to 5 was assigned to each vegetative group: 0 = no species
present, 0.1 = individual or solitary stem, 0.5 = sparse covering, 1 = 0-5% cover, 2 = 5-
25%, 3 = 25-50%, 4 = 50-75%, and 5 = 75-100% (Robblee 2009; Collado-Vides et al.
2007) (Table 1). Canopy height was measured in conjunction with Braun-Blanquet
cover/abundance because it provided a simple and quick measure of the physical
structure of the grass community (Robblee and Browder 2012). For this study, the mean
of all replicate samples per site were used for analyses.
FIAN underwent several modifications in order to better monitor the habitat and
optimize resources. After the 2005 and 2006 collections, the number of quadrat
replicates increased from three to six at a sample site. Greater numbers of samples
increase precision and provide a more accurate picture of the habitat and distribution of
species (Braun-Blanquet 1932). In 2007 it was determined that broad plant groupings
could provide an estimate of overall habitat (nearly comparable to other more time
consuming methods). Therefore, beginning with the fall 2007 collections, estimation of
cover/abundance was expanded to include the three aggregate plant groupings: allvegetation, all-seagrass and all-algae. With the earlier collections spring 2005 through
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spring 2007, aggregate plant groupings were not observed and therefore could not be
calculated from the available cover/abundance scores of the individual species. With
Braun-Blanquet cover/abundance estimates, averaging is only appropriate by species and
scores are not additive between groups. Due to the ordinal scale, once averaged,
abundance cannot be converted back to a cover/abundance index score. The estimate of
overall habitat could only be measured for nine of the fourteen collections (fall 2007